ES 4.3 Lesson Life Change over Time

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• The theory of evolution is demonstrated in the process of

natural selection.

– Explains how life on Earth changes over time due to changes in

the genes of populations

– Most widely accepted scientific theory that explains how life has

changed on Earth

• Population evolution occurs through gene mutation.

– Gives individuals genetic traits that enhance their ability to survive

and produce offspring

4.3 How Does the Earth’s Life Change Over Time?

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• Biological evolution

– Process by which species genetically change over time, occurs

within genes of populations generation to generation

• Natural selection

– Individuals with traits that increase their survivability are more

likely to produce offspring and pass on these traits.

• Fossils (bones, teeth, shells, leaves, seeds, impressions)

Biological Evolution by Natural Selection Explains How
Life Changes Over Time

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• Genetic variability

– Variety of genetic makeup of individuals in population

– Primarily results from mutations (permanent changes to DNA

sequence in genes)

• Can result in heritable traits

• Some helpful, some harmful, some no effect

Evolution Depends on Genetic Variability

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• Adaptation

– Any heritable trait that gives individual some advantage over

others in population

• Genetic resistance

– The ability of one or more organisms in a population to tolerate

chemicals designed to kill the population

– Develops in bacteria and insect species because they rapidly

produce large numbers of offspring (antibiotic-resistant bacteria)

Evolution Depends on Natural Selection

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Evolution by Natural Selection

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• Limiting factors for adaptation:

– Organisms can only adapt to a change in environmental

conditions if the necessary genetic traits are already present in a population’s gene pool.

– Even if a beneficial heritable trait is present in a population, the

population’s ability to adapt may be limited by its reproductive capacity.

Adaptation Through Natural Selection Has Limits